As a positive electrode active material of a lithium ion battery, a lithium-containing transition metal oxide is generally used. Specifically, lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), lithium manganate (LiMn2O4) and the like are used, and in order to improve characteristics (high capacity, cycle characteristics, storage characteristics, reduced internal resistance, or rate characteristics) or safety, using them as a composite is under progress. For large scale application like loading in an automobile or road leveling, the lithium ion battery is now required to have characteristics that are different from those required for a cellular phone or a personal computer.
For improvement of characteristics of a battery, various methods have been conventionally employed. For example, Patent document 1 discloses a method of producing a positive electrode material for a lithium secondary battery, which is characterized in that lithium nickel composite oxide having the composition represented by LixNi1−yMyO2−δ (0.8≦x≦1.3, 0<y≦0.5, M represents at least one element selected from a group consisting of Co, Mn, Fe, Cr, V, Ti, Cu, Al, Ga, Bi, Sn, Zn, Mg, Ge, Nb, Ta, Be, B, Ca, Sc and Zr, and δ corresponds to either a deficient oxygen amount or an excess oxygen amount, and −0.1<δ<0.1) is passed through a classifier to separate those having large particle diameter from those having small particle diameter such that equilibrium separation particle diameter Dh equals to 1 to 10 μm, and those having large particle diameter are admixed with those having small particle diameter with weight ratio of 0:100 to 100:0. It is described that, using the method, a positive electrode material for a lithium secondary battery with various balances between rate characteristics and capacity can be easily manufactured.
(Patent document 1) Japanese Patent No. 4175026